Reconstructing active sites in Ni-Co double hydroxides to enhance electrocatalytic efficiency for nitrate reduction to ammonia

Nitrate-to-ammonia conversion presents an effective method to remediate nitrate pollution while transforming waste into a valuable product and has recently garnered significant attention. Beyond the extensively studied Cu-based catalysts, Co has also garnered significant attention. Identifying the real active sites and elucidating the mechanisms are urgently needed for its development in nitrate reduction. Co3O4, particularly its Co3+ sites, is an established active phase for nitrate reduction and has been 1 extensively studied. However, unlike the deliberate construction of the Co3O4 phase or introducing doping to expose more Co3+ in the previous studies, it was found in this work that the active species above could be generated in Ni-Co double hydroxides in the context of nitrate reduction. The in situ generated Co3O4, especially the spontaneously more exposed octahedrally coordinated Co3+, can significantly facilitate the crucial adsorption of NO3− and thus the following reaction. Furthermore, incorporated Ni sites accelerate nitrate reduction kinetics by promoting hydrogenation, facilitated by their H*-generating capability. This enhanced catalytic activity yields a superior NH3 production rate of 7.05 mmol h−1 cm−2. Besides, a new and more efficient approach for nitrate remediation that focuses on the nitrate sources was proposed and verified through experimentation.